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Study of short-lived resonances in ALICE

Study of short-lived resonances in ALICE. A. Badal à – INFN Sezione di Catania. Contents Physics motivations Some SPS and RHIC results ALICE detector performance Some results from simulated p-p events @14 TeV Summary. 1. A. Badal à- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07.

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Study of short-lived resonances in ALICE

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  1. Study of short-lived resonances in ALICE A. Badalà – INFN Sezione di Catania • Contents • Physics motivations • Some SPS and RHIC results • ALICE detector performance • Some results from simulated p-p events @14 TeV • Summary 1 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  2. Resonances c  (fm) (770) +- 1.3 f0(980) +- 2.6 K*(892)0 K 3.9 (1520) Kp 13 (1020)  K+K- 44  Resonances are strongly decaying particles which have lifetimes of about a few fm/c (i.e resonance~ fireball ) Partial chiral symmetry restoration Interaction of the resonances and/or their daughters with fireball medium Modifications of properties of resonances (peak,width) Why short-lived resonances? Resonances may give information on the dynamics and on the chiral property of the hot and dense matter which is produced in the collision 2 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  3. π- ρ0 π+ ρ0 ρ0 ρ0 π- π+ π- ρ0 + + + π+ - - - Resonances as a probe of chiral symmetry restoration The best probes are resonances reconstructed by their leptonic decay channel since leptons are less likely to rescatter in the hadronic medium. However regenerated resonances from the late hadronic phase feed down into this signal To study chiral symmetry restoration in terms of mass shift and width broadening, resonance decays from the early stage of the medium need to be extracted Hadronic decay channel probes late stages of the collision Leptonic decay channel probes all stages of the collision 3 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  4. In-In@ 158AGeV R. Arnaldi et al. (NA60 Collaboration) Phys. Rev. Lett. 96(2006)162302 NA60 results A significant excess of +- pairs is observed above the yield expected from neutral meson decay. Its shape is consistent with a contribution from +-  annihilation Models based on in-medium  broadening scenario seem able to reproduce data, while moving mass models seem ruled out 4 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  5. Resonances from jets Recently suggestion to study chiral symmetry restoration by comparing resonance production (reconstructed by their hadronic decay) in event classes based on azimuthal distribution respect to jet direction C. Markert, 23rd Winter Workshop on Nuclear Dynamics Big Sky, Montana, USA and SQM07, Levoca (Slovakia) High pT resonances from the away side jet could be modified by the partonic medium, but they are so fast to have low probability to be affected by the hadronic medium 5 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  6. side1 near away side2 (1020) from same/away side in/out of plane near - side side1 • Trigger particle: • hadron pT > 4.0 GeV/c • Associated particle: • resonance (1020) • <pT>~ 0.9 GeV/c away- side side2 No mass shift or width broadening visible Next step:  with higher pt C. Markert, SQM07, Levoca (Slovakia) 6 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  7. Interactions of resonances in hadronic nuclear medium • The yields of resonances detected by their hadronic decay can be influenced by effects of rescattering and regeneration which depends on: • the time between the chemical and the thermal freeze-out • the lifetime of the resonances • the interaction cross-section of the decay particles. Due to the rescattering , resonances may not be reconstructed Pseudo-elastic collisions may regenerate resonances Rescattering Regeneration No interaction The resonances may probe the timescale between the chemical and the kinetic freeze-out 7 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  8. p+p and Au+Au @ sNN=200 GeV Resonance/non-resonance ratio B.I. Abelev (Star Collaboration) nucl-ex 0604019 At RHIC energies thermal models are able to reproduce the ratios of stable particles Deviations from these ratios have been used to estimate the time interval between thermal and chemical freeze-out  (UrQMD) = 13±3 fm/c Suppression of K* and * Lower limit (<4 fm/c, T=160 MeV) from measured K*/K and */ ratio by a thermal model with a rescattering phase (G. Torrieri and J. Rafelski, Phys. Lett. B509 (2001) 239 and C. Market, J. Phys. G. Nucl. Part. Phys. 31 (2005) 1045) 8 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  9. Main observables concerning the study of resonances in pp and AA collisions (*) Extraction of the signal/yields (*) Mass and widths of resonances (*) Transverse momentum and transverse mass spectra (*) Particle ratios Elliptic flow Nuclear modification factors: RCP and RAA 9 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  10. K*(892) πK B.R. ~1 c =4 fm STAR Preliminary STAR Preliminary √sNN = 200 GeV √sNN = 200 GeV √sNN = 200 GeV √sNN = 62 GeV STAR Preliminary STAR collaboration, Phys. Rev. C71, 64902 (2005) 10

  11. Σ(1385)  Λ  B.R. 0.88 c =5.5 fm Λ(1520) pK B.R. 0.45 c =12.6 fm d+Au √sNN=200 GeV d+Au √sNN=200 GeV STAR Preliminary p+p √sNN=200 GeV Au+Au √sNN=200 GeV Star collaboration, Phys. Rev. Lett. 96(2006)132301 11

  12. Φ(1020) K+ K-B.R. 0.49 c =44 fm Au+Au √sNN=62 GeV d+Au √sNN=200 GeV PHENIX STAR Preliminary Au+Au √sNN=200 GeV PHENIX 12 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  13. p+p √sNN=200 GeV Φ(1020) e+e-B.R. 0.000296 c =44 fm d+Au √sNN=200 GeV PHENIX PHENIX S. Huang DIS2007, Munich,Germany Au+Au √sNN=200 GeV PHENIX 13 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  14. STAR Preliminary STAR Preliminary 20-40% dAu 0.6 ≤ pT < 0.8 GeV/c 40-100% dAu 0.6 ≤ pT < 0.8 GeV/c √sNN = 200 GeV √sNN = 200 GeV STAR Preliminary 0-20% dAu 0.6 ≤ pT < 0.8 GeV/c STAR Preliminary 40-80% Au+Au 0.6 ≤ pT < 0.8 GeV/c √sNN = 200 GeV √sNN = 62 GeV ρ0(770)π+ π-B.R. ~1 c =1.3 fm 14 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  15. Mass and widths of resonances • Even in the absence of the phase transition, temperature and density dependent modifications of the mass, width and shape of short-lived resonances are predicted. Possible explanations are: • Dynamical interactions with the surrounding matter (M. Bleisher and H. Stocker, J. Phys. G30(2004)S111, E. V. Shuryak and G.E. Brown, Nucl. Phys. A717(2003)322) • Phase-space distortions • (S. Pratt and W. Bauer, Phys. Rev. C68(2003)064905, R. Rapp Nucl.Phys. A725(2003)254) 15 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  16. STAR Preliminary MC PDG K*0 PDG K*± PDG STAR Preliminary K*  Mass and Width • K*0 pT < 1 GeV mass shift of ~10 MeV observed • K*± and K*0 pT > 1 GeV  mass agrees with PDGfor all systems within errors • Width agrees with PDGfor all systems within errors 16 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  17. Φ  Mass and Width STAR Preliminary • pT > 1 GeV  mass and width agree with MC and PDG for all systems • pT < 1 GeV  mass agrees with MC for all systems within errors • pT < 1 GeV  width higher than MC for all systems  real physics or detector effect? PDG STAR Preliminary PDG 17 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  18.  mass and width d+Au √sNN=200 GeV Au+Au √sNN=200 GeV Au+Au √sNN=62 GeV • Mass and width of  meson reconstructed by KK channel do not depend on centrality • Mass and width in agreement with PDG for all system S. Huang , DIS2007, Munich Germany 18 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  19. Transverse spectra • Particle production in pp collisions dominated by two mechanisms: • soft, thermal-like processes at low pT (exponential shape) • Hard, parton-parton processes at high pT (power-law shape) A unique (Levy) function is used to parametrize the overall shape STAR Coll, PRC71(2005)064902 19 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  20. Cu+Cu @62 GeV Cu+Cu@ 200 GeV K*0 Transverse Momentum Spectra STAR PRELIMINARY STAR PRELIMINARY STAR PRELIMINARY Au+Au @62 GeV S. Dash SQM07 K*0 spectra fitted by an exponential function 20 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  21. →K+K-Spectra STAR Preliminary STAR Preliminary • Change of Φ spectra from exponential in central Au+Au collisions to Levy function shape in peripheral Au+Au  Matter formed in peripheral Au+Au collisions favors hard Φ production STAR Preliminary 21 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  22. NA45 - PRL 96 (2006) 152301] SPS  puzzle NA49%NA50 NA50 reported a  yield measured via dileptons larger than yield determined by NA49 in K+K- channel. Further, the mT spectra exhibit a different inverse slope parameter Pb+Au @E/A=158 GeV NA45 has studied the leptonic and the kaon decay modes of the  meson. • Yield and inverse slope parameter agree in both decay modes • Results are in agreement with the NA49 results 22 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  23. SPS results for →+- (NA60) NA60 In-In (pT < 1.6 GeV/c) NA49 Pb-Pb(pT<1.6 GeV/c) NA50 Pb-Pb(pT>1.2 GeV/c) Difference between NA50 and NA49 was not due to different decay channel Agreement with NA49 when the fit is performed in the same range. T value grows with the centrality of the collision NA60 In-In (pT > 1.1 GeV/c) NA49 Pb-Pb(pT<1.6 GeV/c) NA50 Pb-Pb(pT>1.2 GeV/c) Lower T values and flatter distribution if the fit is performed in the same pT range of NA50. This hints for the presence of radial flow → blast wave analysis M. Floris, SQM07 23 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  24. ΦProduction K+K- and e+e- e+e- K+K- A. Kozlov (Phenix coll.),QM2005 • The leptonic channel yield isalittle higherthan hadronic channel • More accurate measurementis required to confirm if there isbranching ratio modification 24 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  25. ΦK+K-STAR-PHENIX comparison STAR Au+Au @ √sNN = 200 GeV • Φ production  there is a factor of ~2 difference between PHENIX and STAR PHENIX STAR +PHENIX J. Rafelski et al.,Phys.Rev. C72 (2005) 024905 25 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  26. STAR preliminary Resonance suppression (system size dependence) C. Markert, SQM07 Suppression scales with dNch/dy ~ system size 26 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  27. STAR preliminary STAR preliminary Resonance suppression (energy dependence) Life-time [fm/c] K(892) = 4.0  (1020) = 45 S. Dash SQM2007 For K* seems less re-scattering at lower energies in peripheral collisions Lower density  smaller interactions cross section? Shorter hadronic lifetime  less hadronic interactions ? C. Markert, SQM07 27 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  28. Elliptic flow Baryons For KET >1 GeV, mesons and baryons scale separately Mesons S. Adare et al. (Phenix coll.) nucl-ex 0608033 Universal scaling is observed for mesons and baryons when quark number scaling is employed 28 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  29. Elliptic flow for resonances Measurement of flow for meson and baryon resonances is of great interest to further validate the picture sorting of this scaling i.e. that partonic collectivity dominates the transverse expansion dynamics. Au-Au @200 GeV Mass  meson ~ Mass proton v2 of  mesons confirms this universal scaling S. Afanasiev et al. (PHENIX Coll. ) nucl-ex 0703024 29 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  30. K*(892) elliptic flow Using the deviations of the measured flow coefficient v2 from the scaling law given by the quark recombination formalism to probe the amount of hadronic final state interactions • Partonic generation → resonances are produced in a hadronizing QGP → v2 scales with n=2 • Hadronic generation → resonances are produced in the hadronic final state via hadron-hadron scattering →v2 scales with n=4 (K*=K+=2+2) C. Nonaka, et al., Phys.Rev.C69:031902,2004 Au+Au @ 200 GeV Most of K* are produced in partonic phase and only a small quantity is originated in rigeneration (Need more precise measurements) 30 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  31. K*(892) and (1020), (mass ~ mass proton), have RCP values close to the kaon ones. Nuclear Modification Ratios (RCP) for resonances RHIC results have shown as, in the intermediate pt region, nuclear modification factors depend on the constituent quarks rather than on particle mass. 31 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  32. A two components recombination/fragmentation model Recent suggestion by Maiani et al. to use this observable to solve the problem of the real quark composition of some resonances as the fo(980)( or ?) L. Maiani et al., Phys. Lett. B645(2007)138 Nuclear Modification Ratios (RCP) for resonances 32 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  33. Pb-Pb p-p ALICE performance on primary vertex reconstruction Primary vertex in ALICE is reconstructed by means of tracklets in the two innermost pixel layers and by a Kalman vertex procedure for p-p events < 40 m ~ 5 m 33 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  34. ALICE performance on track impact parameter Pb-Pb p-p  <60 m @ pt> 1GeV/c 34 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  35. ITS + TPC Tracking efficiency In ALICE Kalman filter strategy allows a good tracking performance down to very low momenta Momentum resolution pt/pt(%) pt(GeV/c) pt(GeV/c) pt/pt <0.7% for pt<2 GeV/c pt/pt ~ 3 % at 100 GeV/c 35

  36. ALICE performance on particle identification with ITS and TPC at low momenta… and TOF at high momenta… stable hadrons (p, K, p): 100 MeV < p < 5 GeV (few 10 GeV) dE/dx in silicon (ITS) and gas (TPC) + Time-of-Flight (TOF) + Cerenkov (RICH) decay topology (K0, K+, K-, L) K and L decays up to at least 10 GeV leptons (e, m), photons, p0, h electrons in TRD: p > 1 GeV, muons: p > 5 GeV, p0 in PHOS: 1 < p < 80 GeV 36 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  37. 0.6<pt<0.8 GeV/c 1.0<pt<1.1 GeV/c 1.6<pt<1.8 GeV/c 2.0<pt<2.1 GeV/c Mass resolution K*(892) (1020) Mass resolution ~ 1.3 MeV/c2 Mass resolution ~3 MeV/c2 37 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  38. K*(892)0 r0(770) f (1020) Invariant mass (GeV/c2) Invariant mass (GeV/c2) Invariant mass (GeV/c2) Short-lived resonances in ALICE Pb-Pb events studied for PPR 38 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  39. Study of short-life resonances in ALICE Now several activities are going on in ALICE concerning the study of such resonances in pp collisions (using PDC06 events). In particular, resonances reconstructed by their hadronic decay are studied in PWG2. Reconstruction of (1020) by its e+e- decay has also been probed. Catania people have expecially worked on reconstruction of: Resonance K*(892) Φ(1020)*(1520) Decay channel (B.R.) K (~100%)K+K- (49%)N K (45%) Width [MeV/c2] 50.8 4.5 15.6 Life time [fm/c] 3.9 44 13 Started study of +- correlations • Software code development • Test distributed analysis of events • Optimization of reconstruction tools • Background estimation • Efficiency evaluation In next talk results obtained in p-p simulated events at 900 GeV and 14 TeV 39 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  40. Φ(1020): signal

  41. Jet-like azimuthal correlations in -K pairs generated in PYTHIA events at 14 TeV. Background estimation For K*(892)0 BAD agreement between background estimated by event-mixing technique and true background 1 2 40 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07

  42. Summary • Many interesting results on short-lived resonances from SPS and RHIC • ALICE performances (tracking and PID) give us the possibility to do well this kind of physics • We are working to be ready to analyze first data

  43. EXTRA SLIDES

  44. pT= 0 - 0.5 pT= 1.5 - 2 pT= 3.5 - 4 K*(892)0 pT-analysis with realistic PID p-p@14 TeV

  45. K*(892) yield Exp.data PYTHIA Resonance yield Overall number of particles + antiparticles generated by PYTHIA@900 GeV: 1.34 K*(892)/event 0.08 (1520)/event 0.23 Φ(1020)/event A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  46. (780)

  47. K*(892)0 1 GeV/c<pt<2 GeV/c 2 GeV/c<pt<3 GeV/c

  48. Signal extraction (unlike-sign) Inside same event, correlations between K+ and π- candidates K- and π+ candidates Evaluate invariant mass spectrum Example: K*(892)  Kπ (~100%) Mixed-event technique Combinatorial background: Like-sign technique

  49. ALICE PID A common BAYESIAN approach is adopted by every ALICE detector performing PID; The probability w(i|s) to be a particle of type i (i = e,,, K, p...) if a signal s (dE/dx, TOF,...) is detected, is: r(s|i)(Detector response function) conditional probability density functions to get a signal s in a detector, if a particle of i-type hits the detector Ci (particle concentration) a priori probability to find a particle of type i in the detector Probability to be a particle of i-type (i = e, , , K, p, … ), if we observe a vector S= {sITS, sTPC, sTOF, …} of PID signals in different detectors is: Combinated response function

  50. Temperature and lifetime from (1520) / and K*/K G. Torrieri and J. Rafelski, Phys. Lett. B509 (2001) 239 Dependence of the two ratios K*/K and (1520)/, on the chemical freeze-out temperature and time interval between chemical and kineticfreeze-out.Model: termally produced particle yields + rescattering phase. Then regeneration is not taken into account. preliminary 0-20% most central Au+Au C. Market, J. Phys. G. Nucl. Part. Phys. 31 (2005) 1045. (1520)/ = 0.034  0.011  0.013 K*(892)/K = 0.19  0.05 results between : T= 175 MeV =>  = 4-6 fm/c  = 0 fm/c => T= 110-130 MeV  > 4 fm/c for T=160 MeV

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